Nailhead Idle, AFB? - WHAT IS NORMAL?

[XframeFX]

My 3^rd summer of ON/OFF analyzing, measuring, tuning and replacing parts more than once, and still an idle quality NOT befitting a Buick! Some say this idle is normal, really?

Idle is not so bad with the hood up but in the driver’s seat, a resonant thump waiting at a red light in Drive. Not so resonant in neutral but still lumpy with idle set high, set low, doesn't matter.

 

Without instrumenting my Nailhead to death with sensors and transducers, I have trouble determining if it’s a mis-fire or what? Screaming on highest fast idle, appears smooth and at the tailpipes. Again, need to be in the Drivers seat. A brake stand at approx. 1500 RPM, no more resonance but that is not an idle.

 

MPG still absolutely atrocious🆖

 

Work thus far which resulted in no change (except AFB rebuild):

-          Rebuilt AFB (leaking float needle, now tan plugs) with electric heater/functional choke

-          Carburetor base heating holes plugged. Intake heating passage remains open

-          Recurved distributor with electronic trigger and .7 ohm MSD Blaster Coil and Taylor Spiro-Core.

-          Three different sparkplugs/gaps ending with Bosch W9FP at .045”

-          BG 44K fuel additive

-          Roller Timing Chain, degreed original camshaft with 0° Keyway

-          Cleaned out all 16 Johnson Hyd. Lifters and confirmed preload.

-          New Mech. Fuel Pump

-          New 5-Vane Water Pump

-          Heat Riser in full operation, then wired open and left in open position

-          Chased all vacuum leaks including Brake power booster rebuild. Approx. 17" Hg at idle

-          Compression test

-          Combustion chamber borescope

 

Adjusting the 2 idle mixture screws last night with throttle plates closed, I noticed idle became worse opening the passenger side needle from lightly seated!

Adjusting the idle speed high to bypass the AFB idle circuit to allow idling on main jets appears smooth until slipping into the Drivers seat in Drive, still lumpy!

So, next summer, back to addressing the original AFB. An Edelbrock Performer #1411 purchase still remains a possibility but really rather swap to a good Rochester Q-Jet.

 

Consulting Nailhead Owners on this Forum. What is a normal Buick Nailhead idle for my 1963 401 JT?

Thanks☺️

Edited October 23, 2023 by XframeFX (see edit history)

[gungeey]

Few thoughts: 

Your original AFB: A company in FL that sells rebuilding kits with a unique float valve. Marked improvement in idle quality

 

www.daytonaparts.com

 

________________

 

Spark plug wires:  Routing (1/2" from each other, crossed wires, age of wires, dist cap). Run car at night look for jumping sparks along spark plug leads

 

_________________

 

Does the vacuum gauge hold steady?

 

___________________

 

What's the deal with the"thumping"? From crankcase? Random or steady beat?  How many thumps per min?

[Jim Cannon]

My '63 Riv 401 JT has the AFB and it idles very smoothly at a nice, slow idle, especially with the A/C on.

 

You may have a vacuum leak somewhere.

 

Throttle shaft may be worn, giving erratic vacuum leak there (especially since you indicate idle mixture screw on one side affects idle more than other side).

 

What do you know about the seal and gaskets at the base of the carb? Could have a vacuum leak there. Do you have the stainless steel plate in there? I use a gasket on both sides of the plate (even though Buick only called for one).

 

Have you cleaned the PCV valve? Check the PCV hose for a good seal.

 

There is a thermostatically controlled air bleed on the top of the carb that opens when it is hot.  Make sure yours is sealing (press down gently with a pencil eraser).

 

You may just need to get another carb.

 

[NTX5467]

("electric heater/functional choke")  

 

Which AFB is on the car?  Why block the heat track in the manifold?  Yet wire the heat riser open?  Is the carb base gasket the two-piece item (stainless steel plate and then the soft gasket on top)?  Just my experiences (50 years ago), even AC plugs are better than Bosch.  No problem with the wider gap, but .040" might be easier on the coil.

 

Forget all of the sounds, just get the engine adjusted to factory specs.  THEN worry about idle smoothness and "resonances".

 

Which cam is in the motor?  What mpg on a freeway run of 100 miles or so at 60-65mph cruising speed?

 

Just curious,

NTX5467

Edited October 24, 2023 by NTX5467 (see edit history)

[NTX5467]

You may need to learn about the workings of a carburetor.  Reason I say that is that there are some passages which can accumulate hard deposits in them, which can only be removed mechanically, and a carb "rebuild" will not affect, from my experiences.

 

Enjoy!

NTX5467

[EmTee]

Find someone with an ignition O-scope.

[XframeFX]

2 hours ago, Jim Cannon said:

My '63 Riv 401 JT has the AFB and it idles very smoothly at a nice, slow idle

Wow, what I need to hear. Thanks Jim

Again, idling with the hood open and simply driving, all is good. Bad MPG is my observation of the gauge with my minimal mileage. Speedo cable giving problems so no data.

The resonance while waiting in Drive at a red light is my issue. the whole cabin sets up as a low frequency shudder, very annoying. New engine mounts back in 1992 before 30+ year hibernation in garage.

 

As for ethanol resistant parts and that float needle, yes. Wish it showed up in my research. But, I'm ready to dump my AFB which for $400, the rebuilder and his ultrasonic cleaner threw in a NAPA Kit and rattle can'd it silver.

Something about those idle needle valves. Left/right totally different.

I know enough of the AFB in my early years that given a choice, prefer MPG of Q-Jets.

I have carburetor base gaskets on both sides of that plate which I question. Shouldn't it have 4-Holes? The 4 barrels are now interlinked.

 

Original camshaft had >.25" lobe lift so I did not change it

 

Wired open Heat Riser was part of my trouble shooting. This reminds me to render it operational again.

Images are of Autolite AP85 plugs after a summer of driving. Peculiar how #7 & #8 always has residual oil on threads and gasket? #7 less black on other side.

 

Lots of Troubleshooting, no Silver Bullit!:

 

 

 

 

 

 

[RivNut]

A/C equipped cars often develop the “Riviera Rattle.” It occurs when the fuel line and the fuel return line vibrate against each other. Easy fix. Cut some sections of tubing, slice them lengthwise and slide them over one of the fuel lines, then tape the tubing in place.  

[arnulfo de l.a.]

On my original afb carbs idle is adusted through the big brass scew. It regulates the amount of air entering the idle circuit.The idle screws are for regulating the amount of fuel entering the idle circuit. Both the brass screw and idle screws work with each other. The throttle plate should be closed at idle.The factory service manual gives a good explanation on the adjustment procedure 

[XframeFX]

1 hour ago, arnulfo de l.a. said:

On my original afb carbs idle is adusted through the big brass scew. It regulates the amount of air entering the idle circuit.The idle screws are for regulating the amount of fuel entering the idle circuit. Both the brass screw and idle screws work with each other. The throttle plate should be closed at idle.The factory service manual gives a good explanation on the adjustment procedure 

Thanks for the tips. I did try to inspect Idle needle screw seats down the holes a while back. Maybe the screws were turned in hard in my carburetor's past. I always turn them in lightly closed as part of adjusting. Condition of seats was inconclusive.

I'm reverting back to the AFB as the problem after trying all else. Just want to change out assemblies at this point. Will look out for a Q-Jet and intake over the winter. Failing that, an Edelbrock #1411.

 

 

[1965rivgs]

6 hours ago, arnulfo de l.a. said:

On my original afb carbs idle is adusted through the big brass scew. It regulates the amount of air entering the idle circuit.The idle screws are for regulating the amount of fuel entering the idle circuit. Both the brass screw and idle screws work with each other. The throttle plate should be closed at idle.The factory service manual gives a good explanation on the adjustment procedure 

  Dual quad applications only...at least in a Buick.

Tom Mooney

[Lee H]

One possibility that has happened to me, and I didn’t notice being covered in your list: inoperative vacuum advance. If that had a torn diaphragm, you’d get a constant vacuum leak, reduced advance at idle (both of which could cause rough idle), and terrible gas mileage. Easy enough to check.

[NTX5467]

Curious why #1 and #7 have different colorings on the ceramics?  Remind me which ignition system is on the engine?

 

NTX5467

[NTX5467]

How big are those holes in the intake manifold?  Why the 750cfm carb????

 

Getting a new carb can be good in many areas, plus everything will be new and should work and adjust as desired.

 

Start looking for a 3/8" thick carb base gasket with the narrow mounting pattern.  With the heat track passages plugged, no need for the OEM-style items, so you can use normal stuff.  Chrysler AFBs used the narrow pattern until 1968.

 

NTX5467

[60FlatTop]

Just to argue to see the defense, Let's say that six of the cylinders are running lean due to air leaking through the valve guides. Cylinders 1 and 7 have good guides and are fouling due to adjustments to enrich the mixture on the six bad cylinders.

 

Maybe not the answer but when all the problems seem to have been addressed one needs to troubleshoot by thinking "how could I make this happen if I wanted it to".

 

[Jim Cannon]

12 hours ago, XframeFX said:

Thanks for the tips. I did try to inspect Idle needle screw seats down the holes a while back. Maybe the screws were turned in hard in my carburetor's past. I always turn them in lightly closed as part of adjusting. Condition of seats was inconclusive.

I'm reverting back to the AFB as the problem after trying all else. Just want to change out assemblies at this point. Will look out for a Q-Jet and intake over the winter. Failing that, an Edelbrock #1411.

 

 

Get another good AFB that is jetted for the '63 401 with Dynaflow. Don't get an Edelbrock.

 

[carbking]

Not going to get very involved with this, too many modifications to consider; however:

22 hours ago, XframeFX said:

I noticed idle became worse opening the passenger side needle from lightly seated!

 

22 hours ago, XframeFX said:

with electric heater/functional choke

When the automatic choke was downgraded to electric, was the exhaust heat source in the automatic choke housing capped? If not, there would be a vacuum leak on the passenger side only.

 

As to your comments concerning mileage:

 

The Q-Jet is a great carburetor. Low RPM driveability is often better than that of an AFB. Low RPM mileage of the Q-Jet MIGHT be slightly better than the AFB (maybe 5 percent???). If the highway mileage on an AFB differs from that of a Q-jet, assuming both are calibrated correctly for the vehicle in question, then someone needs some carburetor tuning skills.

 

The only time I ever did a direct comparison on highway mileage from a Q-Jet to an AFB resulted in 9.5 percent BETTER mileage on the AFB. This on my Dad's vehicle. Removed the factory Q-Jet and replaced it with a modified AFB.

 

The CARTER AFB is also a great carburetor. The Q-Jet gets improved low RPM driveability from increased venturii air velocity. On the highway, this is not an issue.

 

And to echo Jim's comment above; if you don't find the Q-Jet you wish, would suggest finding another original CARTER AFB designed for Buick, not the other.

 

Jon

[1965rivgs]

8 hours ago, Lee H said:

One possibility that has happened to me, and I didn’t notice being covered in your list: inoperative vacuum advance. If that had a torn diaphragm, you’d get a constant vacuum leak, reduced advance at idle (both of which could cause rough idle), and terrible gas mileage. Easy enough to check.

  This is a great overall point and something I check on every tuneup that I perform. In this specific case, if John is still using the stock carb, the vacuum signal to the advance can is ported so does not affect ignition timing at curb idle. In theory, a bad vacuum diaphragm could present a vacuum leak but in the field, when I have found a bad diaphragm, it introduced no or little leak to upset idle mixture.

  Great advice though, and something that is easy to check and should be done on every tune up.

Tom Mooney 

Edited October 24, 2023 by 1965rivgs (see edit history)

[wmsue]

Since the Nailhead is an externally balanced engine.....any chance the flywheel is not mounted correctly?

That will give you an uneven idle that could be mistaken for a carb problem.

 

RivNut diagnosed this problem with my Buick a few years ago.

 

Good Luck

Bill

 

[XframeFX]

Thanks All for the advise.

I was hoping not to post this topic but after 3 summers, maybe I missed something.

Vac. Adv was replaced. Confident all vacuum leaks are eliminated, even sprayed WD40 at flanges and fittings. I checked intake with a straight edge and carb base on glass pane.

In my other post with smelly fumes out the back, I forgot to mention an enormous amount of water out of tailpipes with engine hot. I'm not a chemist. Hydrogen in the fuel?

Anyway, carb replacement is next. I don't think the rebuilder inspected my original AFB before proceeding. It was ready the next day.

 

 

 

 

Edited October 25, 2023 by XframeFX (see edit history)

[Lee H]

The water out the tailpipes even with the engine hot seems like a big red flag. Are you having to add a lot of coolant?

[1965rivgs]

7 hours ago, XframeFX said:

Thanks All for the advise.

I was hoping not to post this topic but after 3 summers, maybe I missed something.

Vac. Adv was replaced. Confident all vacuum leaks are eliminated, even sprayed WD40 at flanges and fittings. I checked intake with a straight edge and carb base on glass pane.

In my other post with smelly fumes out the back, I forgot to mention an enormous amount of water out of tailpipes with engine hot. I'm not a chemist. Hydrogen in the fuel?

Anyway, carb replacement is next. I don't think the rebuilder inspected my original AFB before proceeding. It was ready the next day.

 

 

 

 

  Water is an expected by product of combustion. I'm not a chemist but I believe the by product increases with a richer condition.

Tom Mooney

[RivNut]

The water out of the tailpipe is more noticeable when the exhaust pipes haven’t warmed up yet. As the pipes get hot, they turn the water to vapor which you don’t see.

[XframeFX]

On 10/25/2023 at 7:35 AM, Lee H said:

The water out the tailpipes even with the engine hot seems like a big red flag. Are you having to add a lot of coolant?

I recently dealt with the Heater Core. Cooling system not an issue.

 

Amazing how all my work on the Nailhead has accomplished nothing.

So, it may run Lean but it starts with a bump of the starter, runs a little rough cold because I kick it off fast idle early but, once warmed-up, runs like a top, no complaints. Just the fuel gauge drops quickly with few miles.

 

 

 

 

 

Edited November 22, 2023 by XframeFX (see edit history)

[NTX5467]

IF the water is clear, it is condensate from the hot exhaust hitting the cold steel in the exhaust system, no more no less.  After the pipes heat up, the hot exhaust flow will evaporate any left in there.

 

About 15 years ago, I could observe new Toyotas as they were driven out of the shop during make ready procedures.  New cars.  After the cars had run a bit, the first main throttle input would usually result in about a cup of water from the tail pipe.  Condensate.

 

IF coolant is leaking due to a compromised/degraded head gasket, the exhaust should smell different AND the radiator hoses should expand after running for a while, usually.

 

If it's running lean, there MUST be a reason.  If the air bleeds on the venturi cluster had been decreased from deposits, that would send the mixture to the richer side of things, not leaner, unless they might have been mechanically enlarged . . . not very possible with a normal rebuild.  OF course, ethanol'd fuel has an optimum mix ratio of about 14.2 to one, whereas non-ethanol'd fuel has always been 14.8 to one.  So E10, by itself, can make things a bit leaner, but usually not enough to compromise things or cause cause additional smells out the exhaust system.  

 

As to "fuels", it used to be that each major refining/brand company had their own tank farms and truck fleet to deliver fuel.  If it was an Exxon station , you KNEW that fuel came from a local Exxon distributor, for example.  It was a higher-quality fuel than the private brand gas station down the street and would consistently work better than that less expensive fuel.  It would take several months of daily metro commutes to work (on that cheaper fuel) before the car would need a tune-up.  I saw that scenario play out several times locally.  The Exxon station owner stated that their Exxon fuel came from Exxon channels, blended at the refinery, whereas the station down the street's fuel was (what is now termed "splash blended") from a generic terminal and the additive package was put into the mix as the gas went into the transport truck.  As things have progressed, I suspect that all fuel is splash blended from generic unleaded fuels.  

 

Even back in the 1970s, I heard stories about how every brands' transport trucks lined up at a fuel terminal (away from the metro area) to fill with gasoline.  Which fed the rumors that "all gasoline, no matter the brand, is all the same stuff".  This seemed to be more prevalent in metro areas away from the main population centers.  As the main population centers usually had larger fuel terminals for specific brands of gasoline.

 

I DO know that the Phillips 66 FliteFuel I bought in Lubbock, TX in 1974 (95.5 pump octane) ran better than the same product I bought in Irving, TX a year later.  Closer to the main refining operation in the TX Panhandle, possibly?  I guess I need to research the current gasoline distribution models to see what's really going on these days?

 

In more current times, with the rise of massive self-service gas stations, plus intense price competition, the consistent prices between "Top Tier" fuels and fuels not labeled as such is miniscule, if any.  Are the private-brand TT fuels the same price as other private-brand non-TT fuels?  Usually the exact same price.  Some of the non-TT stations also sell add-at-the-pump fuel additives, for a fee, too. "Faith" puts them in?  AND, they all operate the same in my computerized car engines!  So, if the TT fuels have certain levels of additives, allegedly costing more, do the non-TT fuels have the same additives at the same levels, but don't go through the TT testing system are are the additive levels a bit lower to not make the TT "cut"?

 

LOTS of unanswered questions!  BTAIM

 

Enjoy,

NTX5467

[arnulfo de l.a.]

Great write up! Thanks

[XframeFX]

On 10/24/2023 at 11:51 AM, Jim Cannon said:

Get another good AFB that is jetted for the '63 401 with Dynaflow. Don't get an Edelbrock.

Well, I mounted a 40 year old Edelbrock  Performer 9625 carburetor from a 350 SBC as-is just to see if any change.

After some quick adjustments, I think my nailhead likes it better. But back in the driver's seat, that thumpy resonance and a noticeable mis-fire. No change.

 

This has been my dilemma. With the hood up and myself troubleshooting, mostly at idle and I ran out of fuel twice in recent months doing this! Everything is fine. Lots of tuning measuring, analyzing, feeling the engine with my hands, a rock solid idle! Tried different steps of fast idle and revving the engine, all good! However, drop the hood and slip behind the wheel reveals my Nailhead's true nature, a rough pig.

Further to this, a recent conversation with an old timer, his comments, "Nailheads have always had a lumpy idle". He is one of many that have commented the same over the 3 years I've been chasing this.

 

I did make some progress with the carburetor swap today. I found a spot under the hood where I could feel a mis-fire at idle that excites a resonance inside the passenger compartment. That is on the A6 AC compressor. Now I can rev the engine with one hand and feel the compressor with the other hand. Still a noticeable miss at various RPMs so, it's not just at idle. A slight beat frequency at higher RPMs but I think that's normal.

 

It has been mentioned before about balance. Transmission shop receipt says they had an issue with a torque converter bolt or nut. I have yet to inspect. If missing, I can see that having a balance issue at speed but not at idle.

 

If a lumpy idle is normal, maybe the new engine mounts I installed in 1990 have gone hard?

If not normal, I need to instrument my nailhead with sensors on each cylinder to find the culprit.

Craving a "refined engine". Can anyone relate to this and possible next step?

 

Thanks!

 

 

 

 

 

 

 

 

 

Edited November 22, 2023 by XframeFX (see edit history)

[EmTee]

Please remind me, have you done a cylinder balance test (i.e., short one cylinder at a time and measure the resulting RPM drop)?  If so, what was the result?

[kegart]

My '63 has a rough idle in drive also. I changed the Rochester to the correct Carter with no change in idle quality. 

I have read that Buick made changes in 401 camshafts in 1962 and mid 1963 to improve idle quality.  I think a early cam may have been installed in my car during a rebuilt by previous owner.

The car runs fine in park and off idle in drive. 

 

Kevin 

Edited November 22, 2023 by kegart (see edit history)

[gungeey]

8 hours ago, XframeFX said:

 that thumpy resonance and a noticeable mis-fire

 

  

"Nailheads have always had a lumpy idle". 

I wouldn't say lumpy , I would say a little jiggle in the idle. 

 

A noticeable misfire would not be normal and needs to be traced.

 

You posted pictures during your timing chain removal. You have what appears to be a virgin block with only the original stake marks on the oil galleys. I remember commenting on the sludge buildup. 

 

Is it a matter of the spark plug 

wires slightly dancing to the beat or is the idle shuddering and stumbling ?

 

I would do a leak down test. Your valves are probably carboned up and one or two not seating perfectly, but good enough. The offending carbon crumb breaks off one and it's a good idle day. The carbon builds up again on another just enough that the valve just doesn't perfectly seat and your pulling the hair out of your head. 

 

You do the leak down test and knowing you, it will send you down a rabbit hole you will not  enjoy. If you look deep enough into a corporation, a newly tiled bathroom or a 60 year old buick engine you can always find something wrong. 

 

Finally, one man's smooth idle is another's shake and bake oven.

 

HAPPY THANKSGIVING

Steve 9236

 

 

 

 

Edited November 22, 2023 by gungeey (see edit history)

[60FlatTop]

I have a 401 and a 425. Both idle smoothly. One man's smooth, dead silent and no matchbooks folded over between dashboard trim.

 

After looking at all the comments again and owning nailheads since 1966 there is one check I would make, one I have done before. Remove the rocker arm shafts and put your finger on the tip of each valve stem. Wiggle it. Since there was no mention of an engine rebuilt I figure a few of them will move around quite a bit. You may also find wear grooves in the rocker arm shafts on the bottom surface. Each rocker arm will slide to let you check.

The wear in the shaft can slightly reduce your valve opening and vary the compression on some cylinders. The worn valve passage, there is no replaceable guide can lean out cylinders or disrupt exhaust flow. Even a small amount of valve stem movement can damage the valve seating surface causing random seating.

It is easy to have a couple of small issues on one cylinder.

 

When I bought my '60 Electra over 20 years ago it had one bad cylinder head that had been damaged by the previous owner. He drilled through the water jacket and broke an EZ out off in the valve cover bolt hole. I replaced the head with a good used one I had. Bill Drake's engine shop cleaned up the valve seats for me. Just a light stone single seat job. I actually hand lapped their job to match the wear to my then 65,000 engine. I am at 90,000 now.

 

I look at it as 8 single cylinders that all need to match, top end and bottom end. Things like valve lift and volumetric efficiency mean even more as the engine wears. All parts will not wear equally so you have to do your repair with the intent of matching the existing wear.

 

Talk about smooth idles, years ago I was at a cruise night 50 miles from home testing a customer's 312 Y-block I had just finished rebuilding. You should have seen the crowd around the open hood when I put my flat bottomed ice cream cone on the air cleaner of the running engine.

 

Details, details, details.

[XframeFX]

4 hours ago, kegart said:

My '63 has a rough idle in drive also. I changed the Rochester to the correct Carter with no change in idle quality. 

I have read that Buick made changes in 401 camshafts in 1962 and mid 1963 to improve idle quality.  I think a early cam may have been installed in my car during a rebuilt by previous owner.

The car runs fine in park and off idle in drive. 

Ah Ha, another with the same symptoms! Thanks for your input Kevin.

The whole passenger compartment has an annoying resonant thump while waiting at a red light in Drive. Once I pull away, all is normal. Also, all is normal under the hood except when I place my hand on the A6 AC Compressor where I feel the same dynamics amplified while seated inside.

Still thinking hard engine mounts and my application of Dynamat on the entire floor pan/toe board might be contributing to the dynamics. I have not ruled out the Dynaflow. Maybe it is amplifying the "Jiggle"?

 

6 hours ago, EmTee said:

Please remind me, have you done a cylinder balance test (i.e., short one cylinder at a time and measure the resulting RPM drop)?  If so, what was the result?

There's a difference when I pull the plug wire off each sparkplug one-at-one time.

 

 

4 hours ago, gungeey said:

would do a leak down test.

Steve, this, I have not done and yes, best left alone😑 Another compression test found all still good.

 

 

4 hours ago, gungeey said:

A noticeable misfire would not be normal and needs to be traced.

Difficult to differentiate between a mis-fire and a "jiggle".

 

Thanks for the round table suggestions all! I have done pretty much all that has been suggested. I'll need to figure out what the next step will be.

 

We already had our Thanksgiving in October. So, Red Thursday followed by Black Friday for us😂

Yes, Happy Thanksgiving!

John B.

 

[NTX5467]

Perhaps the rubber mounts hare hardened a bit, not unusual, but I kind of doubt that's where the roughness is suddenly coming from.  I would be more concerned about that "perceived mis-fire" situation, which seems to be elusive and causing the sympathetic resonance issues.

 

A "lean mis-fire" will be barely felt and might put more hydrocarbons out the tail pipe, as a result.  But not as much as a "full mis-fire" would.

 

As to the "rough idle" issue, the ONE area never addressed is the loading of the torque converter on the engine at idle.  Perhaps a converter with a slight bit looser "high angle" stall speed might be all that's needed?  Of possibly an idle speed up to about 75rpm higher?

 

NTX5467

[XframeFX]

14 minutes ago, NTX5467 said:

Perhaps a converter with a slight bit looser "high angle" stall speed might be all that's needed?  Of possibly an idle speed up to about 75rpm higher?

Ah Ha, my next step, thank-you!

I'll fix the rod in the depressed position and shift to Drive.

 

The variable pitch linkage has not been connected to the Edelbrock Performer carburetor. The rod for it does not travel much so, I'm hoping the transmission rebuild did not dis-able that function. Punching it to WOT, it is hard to detect High-Pitch. Normal for high pitch delay on acceleration?

 

When I "gun" the engine in Park, my Riviera lurches forward against the Park Pawl. Stepping on the brake while gunning the Nailhead, no lurching in Park, just tilting on the Driver's side engine mount.

 

 

 

Edited November 22, 2023 by XframeFX (see edit history)

[EmTee]

2 hours ago, XframeFX said:

There's a difference when I pull the plug wire off each sparkplug one-at-one time.

My question was more specific than that.  Did you attach a tachometer and measure the amount of RPM drop at each cylinder?  I would compare the RPM drops observed for each cylinder. A cylinder that isn't pulling its weight will have a smaller than average RPM drop.

[RivNut]

I cannot find the article but some time ago Denny Manner answered a question in the Q&A section of the Riview.   In his response he stated that the early nailhead cams were fairly radical and because of customer complaints, the camshaft were redesigned to provide a smoother idle.  Perhaps you just have one of the early crammed nailheads.

[NTX5467]

I could find AMA Specs for 1955, 1958, and 1959 364s, plus 1959 and 1966 401s.  I remember reading about the "rough idle" in the 1959 401s, which Buick allegedly made some changes in later model years to seek to correct.  BUT what I found did not really support that.  As to camshaft specs, here's what I found . . .

 

 ++1958 -- 364 2bb4bbl DF  Intake - 34-89-297  Exh - 76-41-297  Lift - .423/.423

 ++1959 -- 364 DF                 Intake - 35-73-288  Exh - 73-37-290  Lift - .443/.439

 ++1959 -- 401 DF                  Intake - 33-77-290  Exh - 75-44-299  Lift - .439/.441

 ++1966 -- 401 AT                  Intake - 28-87-295  Exh - 76-46-302  Lift - .431/.431

 

 --The 1958 364 base ign timing was 5 degrees BTDC @ 400rpm

 --The 1959 401 base ign timing was 12 degrees BTDC @ hot idle speed for the DF, 5 degrees @ 400rpm for the manual trans.

 

According to the number, if ANY engine would have a rough idle, it should be the 364s as it is a smaller engine size with the same cam duration as the 401s, especially the 1959 364 with the higher valve lift.  BTAIM  With the 1966 401 being a slight bit rougher than the 1959, by the duration numbers comparison.  But we might be splitting hairs, as all of the duration and lift numbers are really in the same ball park?

 

For the times, those total duration numbers are a bit larger than other brands' engines tended to use.  The issue with them can be moderated by cyl head flow characteristics and valve sizes.  Which is probably what they tried to do in order to compensate for the allegedly poor port flow on the Nailheads.  Which was noted in a 1967 edition of a Petersen Publications book on USA and Foreign cars.  It noted that with the Nailhead's smaller valves and wilder valve timing, that mid-range torque was increased over a broad rpm band as ultimate top-end horsepower was decreased a bit ty the valve and intake runner sizing.  Which tends to explain the great low and mid-range torque of Buick Nailheads and later Buick V-8s.

 

I won't go into a discussion of "Why" Buick designed the cyl heads as they did, but I suspect that if things were more "Small Block Chevy" in orientation, power would have resulted from the wilder camshafts rather than "torque".  Although the horsepower quoted for the Nailheads (of larger sizes) was competitive, it was not earth-shattering by observation.  With the typical target market demographic of those Buicks, torque was more important than ultimate horsepower, although horsepower was used for advertising purposes.  It also took torque to compensate for the lack of torque multiplication of the DynaFlow transmission, too.  So the DF and more low-end torque (strangled by the transmission) were necessary companions in making Buicks as smooth and responsive as they were . . . at least until the THM400 arrived.  Another story for another time.

 

As to the rough idle, there can be some other things than just camshaft timing events involved.  Hot base idle speed is one, which probably should have been more in the 600-650rpm in "N".  Which could have been helped by a bit more initial ignition base timing.  With the quality of the air/fuel ratio provided by the carburetor in the mix, as well as the equality of air/fuel mixture distribution by the INTAKE MANIFOLD a definite contributor to the situation.  All of these things would have been easier to fix than re-desiging a camshaft.

 

Additionally, upgrades in the ignition system and adding some "fine wire" electrode NGKs into the mix, could also help compensate for some of the mixture differences between cylinders.  A few YouTube videos with that plug in a lawn mower engine with a clear cyl head so the "POW!" of the spark could be seen indicate that the NGK Iridiums deliver longer run-times (on a lawn mower fuel tank full) than other gap designs do.  BUT with some time spent with an ignition point file and some pliers, better results can be had with normal spark plugs, from my experiences.  PM me for details of what I've done over the years.

 

Getting to the carburetor side of things, it has been my observation that as time has progressed, carburetor venturi designs have gotten better with each new version of existing carburetors.  I also discovered (on the OEM AFB on a non-Buick I have), that some time spent with a point file in de-burring the casting flash in the throttle bores and on the outside of the venturis, that more airflow can result.  PM me for information.

 

At this point in time, in the life of the Nailhead engines, there is ANOTHER side issue.  A possible side issue I discovered when I was trying to set the points on my non-Buick, using a dial indicator to set the point gap.  That issue is breaker cam WEAR and how it is not even acros all of the cam lobes.  Different point gaps means different dwell readings for each lobe, which can then mean different base timing effective differences on each lobe, as a result.  Some cylinders might be on 10 degrees BTDC as others are on 8 degrees or even on 6 degrees BTDC, for example.  Might such things, related ot basic production quality control cause a non-glass-smooth idle situation?  Which is where the Pertronix or HEI electronic ignition conversions can come into play.

 

Back when the cars were newer, we didn't worry about such variations.  Much knew they might exist!  So in doing the points, just "choose one" to set the point gap with.  Delco "window" distributors made things easier, with the later dwell meters being a "moving average" of the point gaps and average dwell readings.

 

Another issue can be differences in plug wire resistances, as they are not all the same length.  Ever wonder why modern engines an use "coil on plug" designs rather than unequal length spark plug wires?  Now we're splitting "milli-seconds" in spark production!

 

NOW, we are into the "winter season" when "car projects" happen.  Better than sitting in front of a television display and mindlessly watching binge re-runs of things like "Family Feud" or "The Newlywed Game".  Spending quality time in the garage, where your spouse knows where you are, can result in some progress toward making your cherished vehicle(s) operate and look better than they normally would.  Some wax and polish, too.  Great stress relief!

 

Happy Holidays!

NTX5467
 

 

Edited November 23, 2023 by NTX5467 (see edit history)

[60FlatTop]

14 hours ago, NTX5467 said:

Hot base idle speed is one, which probably should have been more in the 600-650rpm in "N". 

My '60 Electra is about that RPM. Drive in the Dyaflow sucks it down into the high 400s. For 20 years I have been shutting the engine off in Drive then putting it into Park. It can run on sometimes if I don't.

[XframeFX]

On 11/22/2023 at 5:46 PM, NTX5467 said:

As to the rough idle, there can be some other things

It never occurred to me to use my Son's fancy bluetooth scan tool.

My Nailhead is throwing error code "JT401". Googling that code says swap to 6.2LS!😄

Edited November 24, 2023 by XframeFX (see edit history)

[MikeJS]

1 hour ago, XframeFX said:

My Nailhead is throwing error code "JT401". Googling that code says swap to 6.2LS!😄

John, good day.

 

Might be the best option to rid your "idling ghosts"...

 

This '63 (to look like a '65) apparently sold for USD$130K in 2022. Can't imagine how much went into it...How deep are your pockets...??

 

Source: https://bringatrailer.com/listing/1963-buick-riviera-24/

 

Later,